Fabric Improvements for Energy Efficiency in ... - Historic Scotland

1 

Short Guide 

Fabric Improvements 

for Energy Efficiency in 

Traditional Buildings

Fabric improvements for energy efficiency in traditional buildings 

Contents 

1. Introduction 

2 

2. Principles 

5 

3. Fabric Upgrades 

7 

3.1 Roofs and Lofts 

7 

3.2 Floors 

11 

3.3 Windows 

13 

3.4 Doors 

18 

3.5 Walls 

20 

3.6 Chimneys and Flues 

27 

4 . Conclusion 

28 

5. Contacts and Further Reading 

29 

6. Glossary 

32




The Climate Change (Scotland) Act 2009 commits Scotland to some of the 

most ambitious carbon reduction targets in the world, including the reduction 

of greenhouse gas emissions by 42% by 2020; and 80% by 2050 from 1990 

levels (Scottish Government 2009). With around 40% of Scotland’s total carbon 

emissions coming from domestic energy consumption and almost 20% of all 

buildings being traditionally constructed, improving energy efficiency in these 

buildings is key to meeting the national carbon reduction commitments. As a 

government agency, Historic Scotland has been mandated to take the lead in 

research and guidance to improve energy efficiency in traditional and historic 

buildings, as laid out in The Energy Efficiency Action Plan (Scottish Government 2010), 

and further articulated in the Historic Scotland Climate Change Action 

Plan (Historic Scotland 2012). 

Traditional buildings are generally considered to be those built before 1919 

using load-bearing mass masonry walls, with pitched roofs covered in slate or 

another natural roofing material. Windows are generally single glazed with 

timber frames, often in the sliding sash and case pattern, and the buildings have 

internal timber and lime plaster finishes and passive ventilation systems. The term 

‘traditional buildings’ covers a broad range of buildings, not just those referred to 

as ‘listed’, ‘historic’ or ‘heritage’. Scotland has around 400,000 pre-1919 buildings, 

comprising approximately 20% of the total building stock, approximately 47,000 

of which are listed. Such structures include cottages, villas, public buildings and 

commercial buildings as well as tenements, which are prevalent in the Central 

Belt of Scotland (Fig. 1). 

This guide presents a series of practical solutions to improving energy efficiency in 

traditional and historic buildings, through a range of specific fabric improvement 

measures to different elements of a building (specifically roofs and lofts, floors, 

windows and doors, walls and chimneys). Crucially, the methods outlined in 

this report allow the building to continue to function in terms of maintaining 

ventilation and moisture permeability, whilst retaining historic character and 

minimising the visual impact of the changes. The examples given are based 

on a series of trials and pilot projects undertaken or managed by Historic 

Scotland in which energy saving measures were trialled at a variety of traditional 

properties throughout Scotland, including detached rural cottages, tenement 

flats, townhouses and public buildings dating from the 18th, 19th and early 20th 

centuries. The results of these projects are published as a series of Refurbishment 

Case Studies available from the Historic Scotland website, where the specific 

measures are described in more detail. Attention is also drawn to the Historic 

Scotland Technical Papers (also available on our website) which provide detailed 

information on relevant technical issues such as U-value measurements in 

traditional buildings, thermal performance of traditional windows, energy 

modelling and thermal comfort. 

2


01 

This guide does not aim to provide detailed specifications for work to be 

undertaken; rather it seeks to give indicative details of possible approaches and 

potential results. Not all the measures described will be appropriate or possible 

in every case and each situation should be assessed on its own merit with the 

most relevant measures taken based on the specific circumstances, especially the 

historic significance of the building or fabric element. Such considerations should 

always be kept in mind and balanced against possibly more effective savings from 

demand side reductions. The research to date suggests that there is likely to be 

a technique suitable to improve the thermal performance of most traditional 

buildings without adversely affecting their fabric and character. 

Fig. 1 Traditionally constructed 

houses in South West Scotland. 

Whilst this guidance focuses on interventions to the fabric of buildings and the 

upgrades described are broadly in a hierarchy that reflects ease and cost of the 

measures, such work should only begin after other methods of reducing energy 

demand have been undertaken. Improvements to services such as heating 

systems and lighting, and occupier behaviour, will have a significant impact on 

reducing energy use in a building. Furthermore, the field of energy efficiency 

improvements is a rapidly evolving one, and new solutions and approaches are 

likely to emerge over the next few years. Many of the Historic Scotland pilot 

projects described are subject to on-going monitoring, and further results and 

updates will be published in new versions of this guide and updates to the 

Refurbishment Case Studies. 

3



The measures described in this guide are likely to be relevant to most traditional 

buildings and some historic ones; however where a building is listed or in a 

conservation area there may be restrictions on work or additional consent 

processes which will apply. Similarly some procedures may require a building 

warrant. Further information can be found in Building Standards Division Technical 

Handbooks or by contacting local authority Building Standards Departments. In 

all cases it is advisable to contact the local authority Planning Department prior 

to starting any work to establish whether planning permission, listed building 

consent or a building warrant is required. 

Throughout this publication the effectiveness of specific insulation measures is 

indicated using U-values. A U-value is the amount of heat lost (in Watts) per square 

metre of material at a temperature difference of one degree (measured in Kelvin). 

In building fabric work, the lower the U-value, the better the insulation or element 

is performing thermally. All the U-values presented here are actual measurements 

(expressed as W/m 2 K) from the Historic Scotland energy efficiency pilot projects 

(Refurbishment Case Studies). More details on U-values in traditional buildings can 

be found in Historic Scotland Technical Papers 1, 2 and 10: Thermal Performance 

of Traditional Windows, In situ U-value Measurements in Traditional Buildings and 

U-values and Traditional Buildings. 

This document is published jointly with the Energy Saving Trust, who give 

impartial advice on how to reduce domestic energy and carbon dioxide emissions 

in the domestic energy sector, and they should be the first point of contact when 

seeking advice on further upgrade works. They also provide advice on sustainable 

transport and renewable technology, as well as access to funding schemes. This 

advice is delivered through the Energy Saving Scotland advice centre network, 

managed by the Energy Saving Trust and funded by the Scottish Government and 

Transport Scotland. 

4




Research by Historic Scotland supports the view that there are two key principles for 

improving thermal performance in traditional buildings, and these underpin the advice 

given in this guide: firstly that the materials used should be appropriate for the building, 

and in most cases water vapour permeable, and secondly that adequate ventilation 

should be maintained to ensure the health of the building and its occupants. 

Breathable Construction. Traditional buildings are often referred to as being of 

‘breathable construction’ that acknowledges the fact that the materials used for 

their construction have the ability to absorb and release moisture. Such materials 

are often referred to as ‘hygroscopic’. This property is of benefit when seeking 

to buffer the peaks of humidity created through the daily tasks of occupation 

(Fig. 2). Exactly how much water vapour is moved through component materials 

and at what rate will depend on the type of stone (igneous or sedimentary rock 

for example) which the wall is made from, the voids in the wall and the external 

condition of the masonry. In retrofit work, using materials and construction 

methods that are appropriate for traditional buildings will ensure that energy 

efficiency improvements are technically compatible with the building fabric and will 

therefore reduce the risk of damage from inappropriate interventions. Furthermore 

such compatibility will ensure that the upgrades are durable and long lasting. 

Ventilation. Traditional buildings were constructed in a way that allows modest 

air movement through vents, windows, doors and chimneys, circulation through 

rooms, stairwells, and through gaps under floors and behind wall surfaces 

(Fig. 3). This natural ventilation is important for managing moisture accumulation 

and clearing humid or stale air along with other vapours produced in buildings. 

However, when air movement becomes excessive it reduces internal temperatures 

and has a negative effect on thermal comfort. The difficulty is finding a balance, 

because if ventilation is restricted, air carrying water vapour cannot properly 

escape, leading to increased humidity, condensation build-up and undesirable 

consequences such as mould growth. 

MOISTURE MOVEMENT ON MASONRY WALLS 

Ventilation through 

flues and open fire 

Roof covering sheds 

water but permeable 

to water vapour 

Internal 

face 

External 

face 

Fabric heat loss 

Vapour in 

Wind driven rain 

Ventilation 

through eaves 

Limited solar gain 

through windows 

Domestic vapour loading 

Moisture transfer 

to and from 

permeable walls 

Vapour out 

Vapour release 

Moisture 

evaporation from 

permeable walls 

Wall acts as 

heat sink 

Ventilation 

Heating 

Ventilation 

below floor 

Drain 

Solum 

02 Ground 

03 

Moisture transfer from ground 

disipated by ventilation 

Fig 2 A simplified version of water vapour 

movement in a mass masonary wall. 

Fig 3 Air movement in a traditional building. 

5



Consideration of moisture movement and ventilation is of fundamental 

importance when dealing with many older buildings. Provided these factors 

are taken into account, it is entirely possible to successfully increase thermal 

performance and reduce energy use in a traditional building without damaging 

either its character or the building fabric. In seeking to better manage air tightness 

in older buildings, a recent Historic Scotland pilot project achieved an air leakage 

reduction from 18 to 8 air changes per hour, using the measures described in this 

guide (Refurbishment Case Study 7). This is a degree of air tightness, which exceeds 

modern requirements and challenges the assumption that all old buildings have 

to be draughty. 

Maintenance. It should be said that proper and regular maintenance is a 

prerequisite to undertaking energy efficiency improvements in a traditional 

building. If a building is not watertight there is little point in making energy 

efficiency upgrades, and if dampness or excess moisture is already present such 

upgrades may cause further moisture and damage. Furthermore, heat loss through 

a damp masonry wall is higher than from a corresponding dry wall. Details of 

appropriate maintenance measures in traditional buildings are given in a number 

of Historic Scotland publications, including the Historic Scotland Short Guide 

Maintaining Your Home and other publications available on the Historic Scotland 

technical conservation website. 

6


3. Fabric upgrades 


3.1 Roofs and Lofts 

Introduction 

Typically around 25% of heat is lost through the roof of a building; therefore loft 

insulation is a common and effective means of reducing heat loss. Broadly there 

are two approaches to roof insulation: insulating at ceiling level, which creates 

a cold roof space, or between the rafters creating a relatively warm roof space. 

These approaches, along with how to insulate less common roof types, are 

described in detail in this chapter. 

Loft Insulation 

Standard Loft Insulation. When insulating a loft it is often easier to install insulation 

on the horizontal upper side of the ceiling in a loft, rather than between the rafters, 

and this is generally the approach taken by most insulation installers; this gives 

what is termed a ‘cold roof’. In the Historic Scotland trials a vapour permeable and 

hygroscopic material was used to ensure effective humidity buffering and moisture 

management. Suitable materials include rolled material such as sheep’s wool or 

hemp fibre ‘wool’, board-based materials such as hemp and wood fibreboard, and 

loose-fill materials such as cellulose. Generally it is easier to use material supplied 

in flexible rolls, which may also result in a tighter finish. Irrespective of the material 

used, care must be taken to avoid filling the eaves or coom where ventilation 

should be maintained. 

Although every installation will yield different results, Historic Scotland 

trials have shown strong improvements in thermal performance through 

loft insulation, as measured by U-values. In one case the use of sheep’s wool 

insulation improved the U-value from 1.4 to 0.2 (see Refurbishment Case Study 2), 

and in another example hemp fibre wool resulted in an improvement of 1.5 to 

0.2 (Refurbishment Case Study 3). 

Whatever material is chosen it is recommended at least 270 mm of insulation be 

installed to be fully effective. If the attic space is to be used, and a floor is required, 

then this may oblige the deepening of joists through fixing additional timbers 

(Fig. 4). If access is not required then the additional material can be laid across 

the joists. If insulation is already in place with a gap of more than 50 mm to the 

top of the joists, top-up material can be laid between the joists or, if the space is 

less, across the joists. A gap in insulation or a colder spot between insulated areas 

is known as thermal bridge; snugly fitting insulation or laying insulation across 

an existing layer helps to minimise this problem. The access hatch to a loft space 

should also be insulated and draught proofed to prevent warm moist air entering 

the roof space. 

7



COLD ROOF INSULATION 

New fibre board floor 

Additional joist 

Increased insulation 

fill between joists 

Existing joist 

WARM ROOF INSULATION 

04 

05 06 

Existing rafter 

Fig 4 Technique for standard loft 

insulation with a new floor. 

07 

Insulation batts 

laid in 20mm rail 

Existing joist 

08 

Fig 5 Sheep’s wool insulation laid 

between rafters at Edinburgh Castle. 

Note the accommodation of wiring 

above the insulation. 

Fig 6 Low profile roof vents on a slate roof 

following an upgrade to the roof space. 

Fig 7 Technique for insulating roof slopes. 

Fig 8 Wood fibreboard insulation 

fastened to rafters. 

Consideration should also be given to electrical wiring in the roof space. The safest 

and neatest approach is to route electrical cables above the insulation material 

to minimise any risk of overheating (Fig. 5), this will also allow access for future 

maintenance or alterations. In all cases, it is advised to consult a qualified electrician. 

To ensure ventilation at the eaves, a 50mm gap should be left between the end of 

the insulation and the start of the slope of the roof over the wall head. If additional 

ventilation is required it should have minimal visual impact and could be achieved 

through vents at the eaves or on the ridge. Vents on the main roof pitch are also 

possible, with various types available to minimise visual impact (Fig. 6). 

Insulating Roof Slopes 

Rafter Insulation. Roof spaces may be insulated by improving the performance of the 

roof structure itself. Insulation at rafter level results in a warm roof space. Where it is 

not possible to insulate between the joists in a loft, if it is occupied for example, it may 

be necessary to insulate between the rafters in a roof (Fig. 7). This might also be useful 

if warmer attic storage space is required. If there are no linings in the roof space the 

technique is simple, and insulation may be cut to the width of the rafters and held in 

place with timber battens fastened to the cheeks of the rafters. 

In order to best manage water vapour movement a vapour permeable material 

should be used for insulation. For ease of working, a board base material or semiflexible 

batt such as sheep’s wool/hemp fibreboard or a wood and wool mix might 

be most suitable. Any material used should fit snugly between the rafters to avoid 

gaps (Fig. 8) and is best cut in a workshop or in open air. 

In Scotland, most rafters are of sufficient depth (210 mm or 8”) to give room for adequate 

insulation. However, if the rafters are not deep enough for the desired thickness of 

insulation they may be deepened by attaching timber straps to the bottom edge. If some 

form of lining is required then the timber batten holding the insulation may be omitted 

and the insulation held in by the plasterboard or other material. Where there are original 

linings in the attic space, follow the guidance for coom ceilings in the section below. 

8


It is also important to ensure a degree of air movement underneath the sarking boards. 

A gap of 50 mm should be left between the underside of the sarking and the topside of 

the insulation for air circulation. Traditionally, roofs often incorporated ventilation into 

their construction by the inclusion of a ‘penny gap’ between each sarking board. This 

allowed air to circulate throughout the roof structure ensuring dispersal of any water 

blown under the slates in extreme conditions. The use of bitumen based ‘under slate felt’ 

in the post war period has contributed to less draughty attics, but ones where additional 

ventilation is invariably required if insulation work is carried out. Modern roofing 

membranes give a vapour control layer that allows passage of vapour while minimising 

bulk air leakage. If such materials are properly specified, roof vents are not required. 

Coom Ceilings and Dormer Windows 

Coom ceilings are a feature of many Scottish properties where the ceiling is partially 

or sometimes fully part of the pitched roof. Whilst not as easy as insulating a more 

accessible loft, there are likely to be considerable benefits in making the effort to properly 

insulate coom ceilings and dormers, particularly as these are often found in bedrooms. 

Access to the space at the apex of the roof is required, and this is often in the 

form of a small trapdoor; if there is no such access it will have to be formed. 

The separation of the rafters should be measured and sections of insulation 

material cut to that width. These short sections are taken into the space and slid 

down into the void between coom lining and the sarking board (Fig. 9 and Fig. 10). 

As with rafter insulation, a 50 mm air gap should be left between the underside 

of the sarking and the top of the insulation material. 

Another technique is to blow material into the void in a similar way to that 

discussed in section 3.5 (Fig. 11). This will fill the entire void and leave no air gap, 

therefore an open celled material such as bonded polystyrene bead, which allows 

an element of water vapour and air movement, should be used. 

A feature commonly associated with coom ceilings is dormer windows. By their 

exposed nature these are a considerable source of heat loss in a roof bedroom or 

attic space. The cheeks (sides) of the dormer will typically require a thin insulation 

board to be applied, as space is limited. One option would be to use an aerogel 

blanket insulation, which is available in either 5mm or 10mm thicknesses. The 

small area of the dormer ceiling should be insulated in the normal way and is often 

accessible from the roof space above. 

Although every case will be different and will give different results, in one Historic 

Scotland trial the U-value of a dormer cheek was improved from 1.7 to 1.2 by 

using aerogel insulation (see Refurbishment Case Study 6). In the same trial 

improvements to the glazing arrangements of the dormers were also made 

(see section 3.3 of this guide). 

INSULATION OF A COOM CEILING 

Fig 9 Technique for 

insulating coom ceilings. 

Fig 10 Wood fibre insulation 

behind the timber lining 

of a coom ceiling. 

Fig 11 Blowing in bonded 

bead insulation to a coom. 

Existing rafter 

Attic hatch 

Hemp batts slid 

down top of 

existing lining 

09 10 11 

9



Flat Roofs 

Insulating a flat roof presents a number of technical challenges and is harder to 

successfully achieve than the insulation of a loft. The methods and materials used 

should be carefully considered prior to any work taking place. 

Flat roofs generally have some degree of slope (usually around a 1 in 60 incline), 

which is a standard detail to prevent ponding of water. Traditionally flat roofs 

are covered in metal, most commonly lead (although zinc and copper are also 

used), with bituminous coverings becoming common on flat roofs from the mid 

19th century onwards. When insulating flat roofs, in particular those covered in 

a metal, it is important to reduce the risk of condensation by maintaining clear 

ventilation through provision of suitable vents to the outside; otherwise there will 

be condensation on the underside of the roof covering and consequent corrosion 

of the metal and decay in the roof timbers. 

When insulating flat roofs the insulation is usually placed between the joists 

holding the sarking (or ‘decking’ as it is often termed) in place (Fig. 12). This might 

require removal of all, or part of, the ceiling to allow the fitting of the insulation 

between joists. A rigid, vapour permeable insulation material can then be installed 

between the joists and close in with new linings, either reinstating lath and plaster 

or using a modern alternative. The underside of a flat roof should be ventilated 

and a consistent, unobstructed air path of at least 50mm in depth should be 

provided. This technique entails considerable disruption and loss of original 

material in the ceiling and should be considered carefully. Where ceiling heights 

allow, it may be possible to apply insulation directly to the existing ceiling, finished 

with a new lime plaster ceiling over the insulation. 

An alternative method of installing the insulation between joists is to remove the 

roof covering to allow access from above. This is only likely to be practical when 

the roof covering is to be renewed. 

Fig 12 A typical 

underside of a 

flat roof. 

12 

10


3.2 Floors 

Introduction 

A cold floor absorbs heat and can introduce cold air from below floorboards, 

significantly affecting thermal comfort. The thermal performance of both timber 

and concrete floors can be significantly improved as described below, although in 

the case of solid floors this can also involve significant disruption. 

Insulating Timber Floors 

Suspended floors typically lie 300 to 500 mm above the solum, carried by timber 

joists, in a clear span or sometimes supported by sleeper walls. Effective insulation 

is best installed below a timber floor and, as with loft insulation, a vapour 

permeable material should be used to avoid accumulations of moisture, which 

may lead to rot or other forms of damage. Hemp batts and wood fibreboard have 

been shown in Historic Scotland trials to be appropriate for the insulation 

of timber floors. 

The approach with floors is largely dictated by access and quality and value of the 

floor. If the floor is accessible from below with a reasonable crawl space, a stiff or 

semi rigid insulation material can be fixed directly between the joists with timber 

battens, or a softer more flexible material is held by a net fixed between the joists. 

This will allow the floor timbers to remain undisturbed. However, even if there is 

a crawl space, consideration should be given to the working conditions and the 

suitability of activity in restricted spaces. 

Where such access is not possible it will be necessary to lift the floorboards 

to install the insulation. At this stage it may be decided that the disruption and 

potential damage means the work cannot be done. This might be the case where 

there is timber parquet or some other complex layout. If the floor can be lifted, 

rigid wood fibreboard can then be laid on timber runners fastened to the sides 

of floor joists. Careful cutting of the board is required to ensure a tight fit (Fig. 13) 

and this is sometimes best done off site. The lifted boards are then re-fixed 

(Fig. 14). One Historic Scotland trial using an 80 mm wood fibreboard (shown 

in Fig. 13 and Fig. 14) resulted in an improved U-value of the floor from 2.4 to 0.7 

(see Refurbishment Case Study 2). During such work it is prudent to check the 

integrity of the masonry and mortar around the joist ends as they enter the wall. 

Any voids or areas of missing mortar should be pointed up to ensure structural 

integrity and reasonable air tightness. 

Fig 13 Technique for placing 

insulation board between floor joists. 

Fig 14 Floor boards being 

re-fixed following insulation. 

Existing timber floor lifted every 6 boards 

Wood fibre board 

Maintain airflow 

Timber battens fixed 

to existing floor joist 

Existing solum 

13 14 

TECHNIQUE FOR PLACING INSULATION BOARD BENEATH FLOOR JOISTS 

11



In one of the Historic Scotland trials it was found that careful lifting of every sixth 

floorboard allowed sufficient access to fasten battens to the sides of the floor joists 

and the fitting of the insulation board; this considerably reduced disruption and 

potential damage. 

Electrical cables should be routed below insulation or encased in a conduit 

to minimise any risks of overheating. A qualified electrician should be consulted 

in either case. Likewise, the position of water pipes and other services should 

be considered before undertaking insulation work as ambient temperatures 

will be lower. 

All suspended timber floors require free movement of air through the solum void, 

and especially so if the floor has been insulated. The outside ground level should 

be below the ventilation grilles in the masonry and corrosion or vegetation that 

might block airflow should be removed. 

Insulating Solid Floors 

Due to the potential for damage, it is generally recommended that original solid 

floors such as flagstones are left in situ. However, where a floor is required to be 

lifted for another reason, or where the original features have been lost and there is 

a more modern concrete floor, insulation will improve thermal performance either 

through fixing an insulated board on top of the existing floor or by excavating and 

laying a new insulated lime concrete floor in its place. 

Insulation Board. A thin but high performing insulating board fixed on top of a 

concrete floor can greatly improve thermal performance. For example, in an 

Historic Scotland trial the use of a 30 mm aerogel board gave an improvement 

in U-value from 3.9 to 0.8 (see Refurbishment Case Study 6). Aerogel board can be 

supplied in various thicknesses, cut to size and fixed with adhesive (Fig. 15). It is 

important to cut the board to ensure a snug fit at joints and full coverage of the 

floor surface. The base of doors will usually require trimming, resulting in some loss 

of fabric, whilst skirting boards should be removed and reinstated so as to allow 

full coverage of the insulation. A new floor covering will need to be laid over the 

insulated board. 

Fig 15 Aerogel board 

being laid onto a 

concrete floor. Image 

by Changeworks. 

15 

12


Lime Concrete Floors. Older concrete floors are commonly insulated by replacing 

an existing concrete floor with the same material laid over a phenolic foam 

or polystyrene insulating layer. However, whilst thermally effective this is not 

vapour permeable and could therefore lead to water concentration at the base 

of walls. Replacing a concrete floor with an insulated lime concrete floor retains 

the ability to absorb and release moisture whilst improving both the thermal 

performance and the general health of the building. Lime concrete floors have 

proved to be a good base for under floor heating systems and there are a range 

of suppliers who give specifications for the concrete work and the heating coils 

that go in them. Lime concrete however can take time to cure or ‘set’ and needs 

to be protected for a period of around three weeks, and as such might not be 

appropriate in all situations. 

There are two techniques for lime concrete floors: to mix the insulating material, 

for example hemp or recycled glass material, within the lime concrete itself 

and lay as a homogenous whole (Fig. 16); or to lay an insulation layer such as 

lightweight expanded clay aggregate (LECA) onto the solum and place a screed 

of lime concrete on top (Fig. 17, and see also Refurbishment Case Study 8). In both 

cases, the existing concrete floor and subsoil should be excavated to a depth in the 

region of 300 mm, or as required by the material supplier. The soil is then levelled 

and compacted before a layer of geotextile is placed on the ground, and the lime 

concrete floor can be laid using the chosen method. Once laid, lime concrete will 

need to cure and be protected from frost and impact damage normally for at least 

two weeks, although the use of floorboards will allow continued access. When the 

lime concrete has cured it can be polished to a finish, or a floor covering such as 

flagstones bedded in lime mortar can be laid. 

LIME CONCRETE FLOOR WITH LECA* INSULATION 

(* Lightweight Expanded Clay Aggregate) 

Fig 16 Finishing a lime hemp floor 

prior to the relaying of original 

flagstones. Image by Simpson 

& Brown Architects. 

Fig 17 Outline detail for a LECA 

and lime concrete floor. 

100mm 

LECA 0-20mm in 

hydraulic lime mix 

Geotextile barrier 

300mm 

LECA 10-20mm 

laid loose in solum 

Geotextile layer 

16 17 

3.3 Windows 

Introduction 

Traditional glazing is commonly considered draughty or inefficient and therefore 

considered responsible for significant heat loss, yet much of the experienced 

draught can in fact be convection downdraughts from air contact with the cooler 

glass. Historic Scotland has used a range of tests to assess the thermal benefits of 

specific interventions, which can be carried out on traditional windows. The results 

are summarised in Table 1, and presented in detail in Historic Scotland Technical 

Paper 1: Thermal Performance of Traditional Windows. 

13



From a conservation and sustainability perspective, the existing window fabric 

should be retained while upgrading and improving wherever possible. Sash and 

case windows are extremely durable and if maintained correctly will last many 

decades. Many timber windows in Scotland are in their second century. 

A single glazing pane is not a good insulator, with a U-value of around 5.5. 

However many improvements can be made to the thermal performance of a 

window without negatively affecting the fabric or its appearance. Secondary 

glazing is the one of the most effective methods for improving thermal 

performance, reducing heat loss by 63% (U-value of 1.7 in Table 1). Used in 

conjunction with other methods such as blinds and shutters, a reduction in heat 

loss of over 75% can be achieved (U-values of around 1.0). Traditional methods 

such as timber shutters will also significantly improve thermal performance, 

reducing heat loss by 51% (U-value of 2.2). 

Additional thermal improvements can be made using new double glazed units 

which can be retrofitted into existing window frames to minimize the impact 

on the character of the window. These range from thin or ‘slim profile’ double 

glazing to more advance vacuum pane technology. Such intervention may not be 

appropriate in certain situations, for example if the window panes retain historic 

glass. However, should extensive repair or replacement of windows be required 

then this may be a suitable option. 

Improvement Method Reduction in Heat Loss U-value W/m2K 

Unimproved single glazing – 5.5 

Fitting and shutting lined curtains 14% 3.2 

Closing shutters 51% 2.2 

Modified shutters, with insulation set into panels 60% 1.6 

Modern roller blind 22% 3.0 

Modern roller blind with low emissivity plastic film fixed to the 45% 2.2 

window facing side of the blind 

Victorian pattern roller blind, with plain fabric 28% 3.2 

A “thermal” honeycomb blind 36% 2.4 

Victorian blind and closed shutters 58% 1.8 

Victorian blind, shutters and curtains 62% 1.6 

Secondary glazing system 63% 1.7 

Secondary glazing and curtains 66% 1.3 

Secondary glazing and insulated shutters 77% 1.0 

Secondary glazing and shutters 75% 1.1 

Double glazed pane fitted in the existing sash 79% 1.3 

Table 1 Results of U-value testing for improvement measures to sash and case windows. 

14


Blinds, Curtains and Shutters 

Traditional options for reducing heat loss from windows, such as blinds, curtains 

and shutters, can result in significant reductions in heat loss with no impact on 

window fabric (see Table 1). A combination of these systems can reduce heat loss 

by as much as 62%, only 1% less than through the installation of secondary glazing. 

While this will result in reduced light levels, the lowest external air temperatures 

and period of greatest occupancy (and therefore heat loss) is generally at night. 

Roller Blinds. Roller blinds were commonly fitted to windows in the 19th century, 

and in many buildings the original brass fittings are still present in the top corner 

of the sash case. These blinds (Fig. 18) allow privacy during the day, reduced 

penetration of sunlight, and also retained heat. If original fittings remain these 

can be re-used with new fabric; alternatively, new roller blind mechanisms can 

be installed with no damage to the existing window fabric, in a range of modern 

materials with varying thermal or reflective properties. 

Curtains. Full length, lined and well-fitted curtains can control draughts and 

reduce heat loss by up to 14%. Curtains have no impact on existing window fabric, 

although care should be taken to ensure they do not obstruct radiators. 

Shutters. Commonly found in older buildings, timber shutters can reduce heat loss 

of windows by up to 51% (see Table 1). Due to cost however, many rural buildings 

and later tenements were not constructed with shutters and have imitation fielded 

panels made to look like shutters. Restoring painted-up shutters is generally 

straightforward; the benefits are considerable as thermal imaging can reveal 

(Fig. 19). The thermal performance can be further improved through applying 

a thin layer of aerogel blanket, resulting in a 60% reduction in heat loss in trials. 

Such insulation can be fixed to the internal panels of the shutters, and overlain 

with a thin layer of plywood and new beads before painting. 

Where shutters have been removed but the framing and housing remains, a new 

shutter can be made using either traditional joinery techniques (i.e. mortice and 

tenon joints with fielded panels) or by cheaper and quicker modern techniques 

(see Historic Scotland Inform Guide: Timber Window Shutters). If there is no housing 

or shutter case, a shutter can be fixed directly to the sash case, as sometimes seen 

in basements and working areas of older buildings. 

If new shutters are being manufactured then they could be glazed (Fig. 20) to allow 

them to be closed during daylight hours; in effect acting like secondary glazing but 

with the flexibility of a shutter. Such a solution could be particularly beneficial in 

commercial properties, which are occupied during daylight hours. 

Fig 18 Traditional pattern roller 

blinds can result in significant 

reductions in heat loss. 

Fig 19 Thermal image showing 

the benefits of shutters. Image 

by Changeworks. 

Fig 20 Glazed shutters in use. 

18 19 20 

15

FIG. 21 



Brush strip set 

within parting bead 

strip 

d to door 

21 

Brush seal carrier 

based or suitable for 

fitting into existing 

frames including 

bottom sashes 

22 23 

Draught Proofing 

A timber sash and case window in good condition will have very modest air 

leakage, equivalent to air infiltration through a trickle vent and as such should not 

need draught proofing. However where there is excess air ingress through wear 

and tear, draught proofing of sashes can reduce air leakage by up to 80%, although 

not reducing the U-value of the window itself. A range of products is available, 

such as brush or foam strips; the former generally considered to be the most 

effective and durable method. Draught proofing will result in some loss of existing 

fabric in the preparation of the routing channel to hold it in place (Fig. 21), or the 

replacement of the parting beads. It is also possible to incorporate the draught 

proofing into the baton rods, which are commonly replaced several times in the 

life of a sash and case window. 

Fig 21 Common details for 

draught strips fitted to windows. 

Fig 22 Timber framed secondary 

glazing in a dormer window. 

Fig 23 Secondary glazing mounted 

within the staff beads. 

Ventilation may need to be reassessed following draught proofing to avoid 

increased internal humidity and a potential build up of condensation on 

cooler areas such as glass. In cases where draught proofing is part of a wider 

refurbishment requiring a building warrant, the installation of trickle vents may 

be necessary, and listed building consent may apply. For indicative details of 

trickle vents in sash and case windows, see Historic Scotland Short Guide: Sash and 

Case Windows. If secondary glazing is being fitted it may be advisable not to carry 

out draught proofing measures to the mid rail of the window in order to allow 

adequate ventilation. 

Secondary Glazing 

Secondary glazing is essentially a second window installed internally next to the 

original window in order to reduce air leakage and radiant heat losses. They are 

available in a variety of styles and can be effective in improving U-values without 

the loss of existing fabric and with minimal effect on the external appearance. Most 

secondary glazing is made from standard profiles in aluminium, though they can 

be made in timber by a joiner (Fig. 22). 

Frames for secondary glazing can be positioned at any point along the window 

reveal, however it will be most discreet closest to the window. Where shutters 

are present, secondary glazing needs to be mounted within the staff beads of the 

window to allow the shutters to operate (Fig. 23). Some secondary glazing can 

be fixed as non-opening, although consideration will need to be given to 

ventilation requirements. 

16


Some proprietary systems are supplied for installation by the building owner, for 

example polycarbonate sheeting is supplied cut to size and is then fitted to the 

window reveal using magnetic tape (Fig. 24). This system allows for easy removal 

in summer and for cleaning. Such a system should be able to achieve a U-value of 

around 2.4 (see Refurbishment Case Study 2). 

Externally mounted secondary glazing systems are harder to fit to ensure a good 

junction with the existing frame, and may be visually more obtrusive. However, they 

can have a number of benefits including reducing weathering to existing windows 

or the kames of leaded lights, thereby reducing maintenance costs, and can offer 

some protection from vandalism. Such a system may be preferable in very exposed 

locations where the advantages of durability and protection outweigh aesthetic 

considerations. It is advisable to allow ventilation in the gap between the original 

window and secondary glazing to avoid decay or corrosion of the original window 

fabric. The visual impact of external secondary glazing can be considerably reduced 

by matching the paint colour to that of the timber window behind (Fig. 25). 

Double Glazed Units 

Slim Profile Glazing. Where appropriate, glass in sash and case windows can be 

replaced with thin or slim profile double glazing in existing timber sashes. Careful 

assessment of the historic or cultural significance of the original glass is required 

before this work is undertaken. For example, the removal of crown glass should be 

discouraged given the rarity of surviving examples and the significant visual value 

which this glass adds to a building elevation. Where timber frames have suffered 

decay, components can be repaired with new timber sections before the double 

glazed units are fitted (Fig. 26). 

When installing double glazed panels, the check or rebate in the astragal which 

holds the glass is made deeper by around 7mm, and the double glazed units 

(commonly 12.5mm thick) are then fixed into place using synthetic or natural 

putty. Windows should be re-painted before being re-hung, and new sash cords 

and sometimes heavier sash weights are required to allow balanced opening (see 

Refurbishment Case Study 8). 

24 25 26 

Fig 24 Polycarbonate secondary glazing. 

Fig 25 External secondary glazing. 

Fig 26 Original repaired sash with new 

double glazed units. 

17



27 

28 

Although this process can be time consuming with much care required to avoid 

damage to the astragals, it can be a good way to upgrade the thermal performance 

of a building whilst retaining the original timber windows. 

Fig 27 Double glazed panes 

in a new window in Stromness. 

Fig 28 Vacuum panes fitted 

into existing timber sashes. 

New Sashes in Existing Cases. Where the timber of the sash is in poor condition 

and cannot be saved, yet the window case is in good or repairable condition, new 

sashes with double glazing can be made to fit the existing cases following the 

original pattern and pane sizes (see Fig. 27). In some cases a single double glazed 

pane is used for each sash, with applied astragals fastened to the surface of the 

glass, however the long term durability of the applied astragals is not assured. 

Vacuum Insulated Glass. Advanced versions of the double glazed units described above 

are available, which use vacuum technology to create thinner glazing units. These have a 

small metal plug where the air is evacuated, which has some negative visual impact (Fig. 

28). They also tend to be expensive per unit cost, and therefore may be best suited for 

windows with large panes such as late 19th century two pane (‘one over one’) windows. 

3.4 Doors 

Introduction 

Heat loss from doors can be reduced by either draught proofing around the door 

or insulating the fabric of the door itself. These techniques are normally used on 

external doors as there is usually little need to insulate internal doors unless there are 

significant heat differentials between rooms. Draught proofing around the edge of 

the door, the letterbox and covering keyholes can help to considerably reduce heat 

loss. Draught proofing may not be suitable where the door is of particular heritage 

value or when upgrading a fire door, and advice should be sought in these cases. Some 

indicative details for common door draught proofing are shown in Fig. 29. 

18


Spring or V strip 

pinned into 

a door frame 

Brush strip 

applied to 

door 

Carrier based seal 

which is pinned to 

the door frame 

29 

Improvements to Panelled Doors. Whilst timber door frames perform well thermally, 

improvements can be made to the panels of doors which are often made of thinner 

wood. Insulation can be fitted in a single layer, or multiple thinner layers, to the 

inside of the door panels, maintaining the external character of the door (Fig. 30). 

Fig 29 Common draught 

proofing details for doors. 

The insulation material used should allow vapour permeability and be thin enough 

not to significantly alter the appearance or configuration of the door. The material 

DOOR INSULATION 

should be fitted using an adhesive rather than nails or screws, before applying a 

thin layer of plywood and fixing new beads or moulding prior to painting (Fig. 31). 

In the example shown in Fig. 31, an improvement in U-value from 3.9 to 0.8 was 

achieved (see Refurbishment Case Studies 1, 6 and 8). 

Toprail 

Timber bead to 

hold plywood 

Aerogel insulation 

5mm plywood 

cover 

Midrail 

30 

Existing panel 

Upgraded panel 

31 

Fig 30 Technique for 

insulating door panels. 

Fig 31 A section of an 

insulated tenement door 

prior to painting. 

19



3.5 Walls 

Introduction 

Recent Historic Scotland research has shown that modest intervention to the 

internal surface of mass masonry walls can considerably improve their thermal 

performance. This improvement in thermal performance can be achieved using a 

number of methods. Some of these methods are in line with good conservation 

practice, are relatively cheap and less disruptive to the occupants, and also allow 

the retention of existing internal linings and finishes. 

As discussed in section 2, traditional mass masonry walls allow moisture vapour 

movement through the fabric. Traditional internal renders made from hygroscopic 

materials also assist in buffering humidity produced by domestic occupation, and 

it is therefore vital that any insulation (as well as any finishing material applied over 

the insulation) allows this movement of water vapour to continue. 

In considering a wall insulation of any type, the situation and exposure of the 

building to prevailing weather, especially wind driven rain, is important. Walls 

with high exposure should probably not be treated, without full consideration of 

their integrity and performance. In such cases, resources may be better spent on 

external detailing improvements to better manage wind driven rain. 

Internal Upgrade Options. There are four broad approaches to the application of 

internal insulation to mass masonry walls: 

• Insulation blown behind existing wall linings 

• Insulation applied on existing wall linings 

• Insulation applied directly to masonry or plaster 

• Insulation held in place by timber framing 

The method used should be largely determined by the extent and condition of the 

original fabric that remains. Where lath and plaster survives, there will normally 

be a cavity between this and the masonry wall. Where original linings have been 

lost, more recent dry linings can be removed and replaced with insulation, either 

directly to the masonry (‘on the hard’) or, where space allows, the wall can be 

framed with timber to hold insulation in place. In general, thinner materials such 

as calcium silicate based insulation board and aerogel based blanket are best 

applied directly to the masonry, whilst thicker materials such as wood fibreboard 

and hemp board are best held in place with framing. 

It is important to avoid thermal or cold bridges when insulating a wall. These are 

formed where different elements of the building structure are present which 

lose heat at a more rapid rate, for example where thinner walls are present in a 

splayed window reveal. The presence of surfaces of lower temperature can lead to 

condensation, and possible decay of materials. In practice, it is almost impossible 

to fully avoid this when retrofitting insulation, but steps should be taken to 

minimise the risk. 

20


Materials. As mentioned previously, it is vital to choose an appropriate vapour 

permeable material to avoid creating a vapour barrier which could lead to build up 

of moisture and associated decay within the wall. A natural material such as hemp 

or wood fibre board, a wood/wool mix, blown cellulose or sheep’s wool is most 

likely to achieve this. Non-vapour permeable products, while thermally effective, 

may not be appropriate in traditionally constructed buildings as they could lead 

to moisture concentration and subsequent fabric decay. 

Site Trials. An Historic Scotland trial in a Glasgow tenement monitored moisture 

levels within the wall fabric following the installation of five different vapour 

permeable insulation types. The results of the first year of monitoring are 

summarised in Table 2 below, showing the average relative humidity levels over 

a year long monitoring period at the point of interface between the wall and 

the insulation and at a depth of 50 mm into the stone (see also Refurbishment 

Case Study 4). None of the insulation materials trialled are shown to be causing a 

damaging build-up of moisture at the interface between the insulation and wall, nor 

within the wall fabric itself. In three cases (aerogel board, hemp board and wood 

fibre) the relative humidity was higher than that in the room (only considerably so 

in the case of wood fibre), but all were within limits considered safe. Humidity for 

blown cellulose and bonded bead was lower at the interface and within the fabric 

of the wall than in the room. Importantly, whilst the results below are averages, in 

no cases did humidity rise significantly over the monitoring period. These results 

begin to prove that insulation can be safely applied directly to mass masonry walls 

without a vapour barrier. Further monitoring will continue over a five year period 

at this and other research sites to examine this issue in greater depth. 

Insulation Type 

Average Relative Humidity of 

Room (%) 

Average Relative Humidity at 

Interface Between Wall and 

Insulation (%) 

Average Relative Humidity 50 

mm Into the Wall Fabric (%) 

100mm Hemp board 52.1 65.2 66.6 

80mm Wood fibreboard 20.7 61.7 58.9 

50mm Blown cellulose 21.9 14.8 14.3 

50mm Aerogelboard 45.9 64.4 63.3 

50mm Bonded polystyrene bead 58.3 16.4 15.8 

Table 2 Relative humidity readings recorded at the wall/insulation interface in the five flats. Data from Historic Scotland Refurbishment Case Study 4. 

21



Thermal improvement of internal walls will be influenced by the type and thickness 

of material chosen and the initial conditions and materials present. Historic 

Scotland trials have found that good results are possible when insulating mass walls. 

The results using a range of insulation materials are summarised in Table 3 below. 

Insulation Type Method of Installation Unimproved U-value Improved U-value 

80mm Wood fibre Applied between timber framing 1.1 0.19 

100mm Hemp board Applied between timber framing 1.1 0.21 

40mm Aerogel board onto 

metal straps 

Applied onto metal straps 1.1 0.22 

100mm Cellulose fibre Sprayed damp onto masonry 1.1 0.28 

50mm (approximately) Bonded 

polystyrene bead 

Blown behind existing wall 

lining 

1.1 0.31 

30mm Aerogel board Applied onto metal straps 1.1 0.36 

100mm Wood fibre Applied between timber framing 2.1 0.4 

50mm (approximately) 

Cellulose bead 

Blown behind existing wall 

lining 

1.3 0.6 

10mm Aerogel blanket Applied directly to masonry 1.6 0.9 

50mm Calcium silicate board Applied directly to masonry 2.1 1 

Table 3 Pre and post U-values for different insulation types. 

The following sections describe in further detail the four broad approaches 

outlined above which can be taken to insulate masonry walls, and the methods 

and materials which may be appropriate for each. 

Insulating Behind Lath and Plaster 

Blown materials are used to improve the performance of lath and plaster wall 

finishes in a similar way to the techniques used in cavity wall insulation. This allows 

retention of existing linings and minimises disruption to historic material as well as 

reducing disruption to the occupants (Fig. 32). Using this method there is however, 

a significant reduction in the ventilation of the cavity between the lath and plaster 

and the masonry wall, and it is therefore vital that a vapour permeable, ideally an 

‘open-cell’, material is used to allow modest movement of air and water vapour 

whilst preventing draughts behind the laths. Appropriate materials could include 

blown cellulose, polystyrene bead, perlite and a water based foam. 

SOLID WALL INSULATION 

Holes every metre 

Fig 32 Technique 

for blown insulation 

behind a lath and 

plaster lining. 

Blown in material 

Existing lath 

and plaster 

Redecorate with 

vapour open lining 

Material blown-in 

via 25mm holes 

32 

22


When inserting or blowing this material behind lath and plaster wall linings in 

Historic Scotland trials, great care was taken to ensure that the wall was initially 

dry and able to stay dry by retaining or improving water vapour permeability. The 

role of external maintenance is vital in achieving this, which includes for example 

the proper functioning of rainwater goods such as gutters and downpipes. 

Modern external finishes such as cement render may compromise water vapour 

permeability, but where practicable all steps should be taken to ensure the best 

level of permeability possible. In most domestic buildings this is likely to require 

the removal of textured wallpapers and vinyl paint finishes revealing the bare 

plaster. Prior to installing the insulation, gaps in the base of the wall should be 

closed off to prevent material falling into voids below. This is achieved by removal 

of the skirting boards, and packing the lower part of the wall with a fibrous 

material such as wood wool or rough hemp fibre. Holes in the plaster are then 

made every metre to permit access for the blower nozzle. The insulation material 

is then blown in from successively higher levels until the ceiling is reached (Fig.33). 

A thermal imaging camera can be used to ensure the insulating material has filled 

all the voids, or alternatively a borescope can be used (Fig. 34). Any missed areas 

can then be filled, and the holes filled prior to redecoration or touching up. Lining 

paper applied with a water based paste provides a good base for the application 

of traditional distemper, clay or mineral paint or other permeable finish when redecorating 

after the works. 

Although the U-values achieved will vary considerably depending on which 

material is used, and factors such as the depth of void which exists between the 

masonry and wall lining, Historic Scotland trials have shown the use of bonded 

polystyrene bead in this way resulted in a U-value improvement from 1.1 to 0.32, 

and by using blown cellulose an improvement from 1.3 to 0.6 in one trial, and 1.1 

to 0.29 in other (see Refurbishment Case Studies 2 and 4). 

Fig 33 Cellulose fibre 

being blown behind 

lath and plaster. 

Fig 34 Inspecting the 

void with a borescope 

during the insulation 

process. 

33 34 

23



Insulation Applied Onto Existing Lath and Plaster 

Where concerns exist over intervention in the void behind the lath and plaster, 

the addition of a thin layer of insulation may be appropriate. While some thin 

insulation products have been available for some years, mainly as a way of 

controlling condensation in modern buildings, newer high performing aerogel 

products can be applied to the surface of lath and plaster linings to improve 

thermal performance, while allowing the air gap behind the plaster to function 

unchanged. This might be suitable where the wetting cycle of the wall is of 

concern, such as in an exposed location. With a total thickness of 25 mm, this 

measure will not significantly affect room proportions, cornice details and other 

finishing elements. 

Aerogel-based insulation comes as either a board or a ‘blanket’ supplied as a roll. 

The blanket can be supplied in 5 mm or 10 mm thicknesses, and also has the 

advantage of being able to be used on curved surfaces. It is fixed to the existing 

wall finish with an expanded steel mesh using thermally decoupled expansion 

fasteners (required to prevent thermal bridging). During the installation shown in 

Fig. 35, a timber bead was applied below the existing cornice to maintain a neat 

junction. Two coats of plaster are then applied on the mesh and finished with 

a permeable paint finish. The total thickness of this measure is in the region of 

25mm. Aerogel blanket has given a range of thermal improvements in Historic 

Scotland trials, including one improvement in U-values from 1.6 to 0.9 (see 

Refurbishment Case Studies 1 and 3). 

Material Applied Directly to Masonry Without Framing 

Where a wall was originally plastered ‘on the hard’ there is an opportunity to 

insulate directly onto the existing plaster surface, minimising the impact on the 

room proportions and facings. Historic Scotland have trialled a calcium silicate 

board in this situation, although wood fibre based products and other appropriate 

insulation materials can also be directly fastened to a mass wall. The calcium 

silicate board is available in a range of thicknesses to suit site conditions and the 

thermal improvement sought. Existing wallpaper and paint should be stripped 

from the masonry (Fig. 36) and a vapour permeable adhesive applied to the wall 

before the insulated panels are fitted in place (Fig. 37). 

The board is finished with two coats of plaster and a permeable paint finish. In 

one Historic Scotland trial this method improved U-values from 2.1 to 1 (see 

Refurbishment Case Studies 3 and 6). 

Fig 35 Aerogel insulation fixed 

to surface of the existing lath 

and plaster with a steel mesh 

prior to application of plaster. 

Fig 36 Removal of previous 

decorative layers prior to 

application of the board. 

Fig 37 Application of the 

insulating boards. 

35 36 

37 

24


New techniques, as yet untested by Historic Scotland, are being developed using 

an insulated lime plaster applied internally ‘on the hard’. Such an internal finish 

might be suitable in some situations, especially in vernacular buildings and service 

areas where plaster on the hard is common. To achieve reasonable thermal 

improvement, 50 – 80 mm of the insulated plaster is required and it also requires 

total removal of existing finishes. The material is batched up and applied in layers 

to the desired thickness and plastered to give a smooth finish (Fig. 38). Limewash 

or distemper are used for final decoration. 

Insulation Applied Within Framing 

Where original lath and plaster wall linings have been removed or are badly 

damaged, there may be space to fix new timber strapping or framing to hold a 

thicker board-based insulation material such as hemp, wood fibre or aerogel 

boards. The use of timber framing to hold insulation is a fairly well established 

technique in construction and there is a wide choice of appropriate vapour 

permeable insulation materials, available in rigid boards or more flexible batts. 

The depth of the framing is dictated by the thickness of the insulation products 

and this should be considered in relation to room features and available space. 

The material is placed within the framing and closed in behind plasterboard or 

clay board (Fig. 39), showing a hemp fibre bat behind a clay board. 

38 

Fig 38 Insulated lime 

plaster prior to limewashing. 

Image by Eden Lime. 

Some proprietary systems, such as the aerogel board, use a metal frame (Fig. 40). 

Alternatively vertical timber studs are fixed to the wall and damp-spray cellulose 

is applied directly between the framing (Fig. 41). Once dry the cellulose is then 

‘planed’ flush to the strapping and covered with clay board or plasterboard. 

The U-value improvement with this method will vary depending on thickness and 

type of materials used. Historic Scotland trials in external walls found that 100mm 

of wood fibreboard improved the U-value of the wall from 2.1 to 0.19; 100mm 

hemp board from 1.1 to 0.22; and 50mm aerogel board from 1.1 to 0.23 (see 

Refurbishment Case Studies 4, 6 and 8). 

39 40 

41 

Fig 39 Hemp fibre 

insulation with clay boad. 

Fig 40 Aerogel board 

mounted on steel framing. 

Fig 41 Cellulose insulation 

being applied wet. 

25



42 43 

44 

External Insulation 

In some situations insulating material can be applied to the external face of the 

masonry. Due to aesthetic considerations and difficulties in application, this 

approach is unlikely to be appropriate to many traditionally constructed buildings, 

for example where there is high quality ashlar work or a visually attractive façade. 

There may also be difficulties in detailing such insulation, for example at window and 

door reveals. Fig. 42 gives an indication of the visual effects of external insulation. 

Where a building has previously been rendered or harled, the application of an 

insulated replacement may be appropriate and practicable (Fig.43). This may be 

especially beneficial where an impermeable cement-based render is failing and 

its removal may benefit the building fabric through improved moisture handling. 

In many cases in Scotland, the gables and rear elevations of buildings are often 

architecturally less complex and may suit a thin form of external insulated render. 

Fig 42 The visual impact of 

external insulation. 

Fig 43 This gable end, in need of 

maintenance, and showing the 

remains of a lime render, is well 

placed to receive an appropriate 

form of thin external insulation. 

Fig 44 A wood fibreboard external 

render system applied to a pend 

in Glasgow. 

At present however, with materials and techniques available today, external 

insulation will be expensive to install and may only be effective where relatively 

large areas are being treated in an area based upgrade scheme. There will be 

situations where conventional external insulation is appropriate and, as with other 

interventions in this guide, it should be moisture vapour permeable. Lime based 

materials of this type are in their infancy and have yet to be trialled. Boards and 

spray-applied materials that do not allow a degree of moisture movement through 

the structure should not be used as these could result in a build up of moisture in 

the fabric of the wall. It should be noted that a building warrant is required for any 

application of insulation to an external wall. 

For external insulation a board and render system such as the wood fibreboard 

may be appropriate if it allows the vapour permeability of the wall to be 

maintained. Fig. 44 shows a wood fibreboard 40 mm in thickness applied to the 

walls and ceiling of a pend beneath a tenement in Glasgow. The boards need 

to be protected from direct moisture, and special edge and drip detailing is 

required to keep driven rain away from the board. Such board-based external 

insulation generally requires a render system to make it fully weather proof and it 

is important that this is also vapour permeable. The level of thermal improvement 

gained from the insulation shown in Fig. 44 resulted in a U-value reduction of the 

wall from 1.3 to 0.4 (see Refurbishment Case Study13). 

26


3.6Chimneys and Flues 

Introduction 

Fireplaces (or chimneypieces) are important in providing ventilation in traditional 

buildings. The action of moving air within the flues draws air through the rooms 

and assists in removing any concentrations of moisture in the masonry, especially 

at exposed gable ends. Closed flues are therefore prone to an accumulation of damp 

if air flow is restricted and the permanent closing up of hearths is not advisable. 

Closing Flues 

If a fireplace is no longer used and there is a desire to close it off to reduce 

draughts, it is important that some form of air movement is retained. An inflated 

‘chimney balloon’ (Fig.45), can be used to minimise draughts in the winter period, 

and can be removed in the summer, when increased airflow, and the associated 

cooling, might be required. 

A chimneypiece can also be temporarily closed off with a hearth board, fitted 

over the opening (Fig. 46). All chimney heads, whether in use or not, can be 

fitted with a conical vented cowl (Fig. 47), to keep out rain and birds while 

remaining in use. 

Chimneys may be able to be re-used for new heating appliances such as some 

modern enclosed grates (Fig. 48), wood burning stoves and biomass micro-renewable 

systems. In this case, a thorough flue inspection should be carried out and any repairs 

undertaken to the masonry and the lining; the chimney may also need to be re-lined. 

Professional advice should be sought in all cases. 

45 46 

47 

48 

Fig 45 A chimney balloon as 

used to temporarily close off 

chimney flues. 

Fig 46 A hearth board used 

to temporarily close off a 

fireplace. 

Fig 47 A cowl used to keep 

chimneys dry, but ventilated 

and free of birds. 

Fig 48 An existing Edwardian 

cast iron inset, retrofitted 

with a glazed grate for more 

efficient burning. 

27


4. Conclusions 

4. Conclusions 

49 

Traditionally constructed buildings are capable of being upgraded to give a much 

improved level of thermal performance. This can be achieved by interventions 

sympathetic to both their appearance and performance. Improvements can, 

in many cases, be achieved without resorting to the wholesale loss of original 

building fabric or the use of materials which are incompatible with the character of 

the building, as has been demonstrated in the Historic Scotland trials programme. 

One of the trials, a project in association with Castle Rock Edinvar Housing 

Association (Fig. 49), won the Carbon Trust’s Low Carbon Retrofit Award in 2012. 

Fig 49 The award 

winning project 

in Edinburgh. 

By carefully considering the methods and materials described in the guide, the 

thermal performance of traditionally constructed buildings can be significantly 

improved. This will help to ensure that an important element of the nation’s 

building stock has a viable future and can play its part in creating a sustainable 

and low carbon Scotland. 

28


5. Contacts and further reading 


Contacts 

Historic Scotland: 0131 668 8600 www.historic-scotland.gov.uk 

Historic Scotland Conservation Website – Knowledge Base. 

www.historic-scotland.gov.uk/conservation 

Society for the Protection of Ancient Buildings (SPAB): 020 7377 1644 

www.spab.org.uk 

The Energy Saving Trust: 0800 512 012 www.energysavingtrust.org.uk 

Reading 

Changeworks (2008), Energy Heritage: A guide to improving energy efficiency 

in traditional and historic homes, Edinburgh: Changeworks 

www.changeworks.org.uk/content.php?linkid=373 

English Heritage Saving Energy guidance: 

www.climatechangeandyourhome.org.uk/live/saving_energy.aspx 

Historic Scotland (2012), A Climate Change Action Plan For Historic Scotland 

www.historic-scotland.gov.uk/climate-change-plan-2012.pdf 

Hughes P. (1993), The Need for Old Buildings to Breathe, London: SPAB 

Scottish Government (2009), Climate Change (Scotland) Act 

www.legislation.gov.uk/asp/2009/12/contents 

Scottish Government (2010), Energy Efficiency Action Plan 

www.scotland.gov.uk/Publications/2010/10/07142301/0 

The Prince’s Regeneration Trust (2010), The Green Guide for Historic Buildings, 

London: TSO 

Urquhart D. (2007), Conversion of Traditional Buildings, Edinburgh: Historic 

Scotland 

Walker S. (2012), Energy Use in the Home, Edinburgh: Scottish Government 

Wright, G.R. and Howieson, S.G. (2009), Effect of improved home ventilation 

on asthma control and house dust mite allergen levels, Allergy Vol. 64, No. 11, 

pp. 1671-1680 

29



Historic Scotland Technical Papers 

Technical Paper 1 – Thermal Performance of Traditional Windows 

Technical Paper 2 – In situ U-value Measurements in Traditional Buildings 

Technical Paper 6 

– Indoor Air Quality and Energy Efficiency in Traditional Buildings 

Technical Paper 7 – Embodied Carbon in Natural Building Stone in Scotland 

Technical Paper 9 – Slim-profile double glazing 

Technical Paper 10 – U-values and Traditional Buildings 

Technical Paper 12 – Indoor Environmental Quality in Refurbishment 

www.historic-scotland.gov.uk/technicalpapers 

Historic Scotland Refurbishment Case Studies 

Refurbishment Case Study 1. 

Windows and Wall Upgrades to Five Tenements, 

South Side, Edinburgh. 

Refurbishment Case Study 2. Wall, Floor, Roof Space and Glazing Upgrades, Well O’ 

Wearie Cottage, Edinburgh. 








Wall and Roof Space Upgrades, Wee Causeway 

Cottage, Culross, Fife. 

Wall Upgrades to Six Tenement Flats, Sword Street, 

Glasgow. 

Roof Space and Glazing Upgrades, Tenement, 

The Pleasance, Edinburgh. 

Wall, Floor, Door, Roof Space and Glazing Upgrades, 

Kildonan Cottage, South Uist. 

Wall, Floor, Roof Space and Glazing Upgrade, 

ScotstarvitTower Cottage, Fife. 

Wall, Floor, Roof Space and Glazing Upgrades, 

Garden Bothy Cottage, Cumnock, Ayrshire. 

Roof Space Upgrade, Leighton Library, Dunblane. 

Refurbishment Case Study 10. Wall Upgrade, Tenement, Govan, Glasgow. 

Refurbishment Case Study 11. Wall, Door and Glazing Upgrades to Two Tenements, 

Rothesay, Isle of Bute. 

Refurbishment Case Study 12. Roof Space and Glazing Upgrades, Terraced House, 

Newtongrange, Midlothian. 

Refurbishment case study 13. Wall and Window Upgrades, Whitevale Street, 

Glasgow. 

30


Historic Scotland Guides 

Short Guide: Maintaining Your Home 

Short Guide: Sash and Case Windows 

INFORM: 

INFORM: 

INFORM: 

Shutters 

Glass and Glazing 

Flat Roofs 

http://conservation.historic-scotland.gov.uk/publications 

31


6. Glossary 

6. Glossary 

For more information on Scottish building terms, see Dictionary of Scottish 

Building by Glen Pride, Rutland Press 1996. 

Aerogel: 

Architrave: 

Astragal: 

Batt: 

A synthetic porous material derived from a gel, in which 

the liquid component of the gel has been replaced with 

a gas, resulting in a material with very low density and 

thermal conductivity. 

The mouldings framing a door or window. 

The bars in a window that separate and hold the individual 

panes of glazing. 

Semi rigid insulation board. 

Calcium silicate board: A rigid, micro porous mineral board. Its high capillary action 

assists in humidity regulation. The nature of the material 

means that mould cannot form on its surface. 

Cellulose insulation: 

Chimneystack: 

Condensation: 

Cold roof: 

Cornice: 

Coom ceiling: 

Cold bridge: 

Dew point: 

Draught proofing: 

Formed of cellulose fibre commonly derived from recycled 

newspapers. It can either be used blown in to cavities, laid as 

loose fill or applied directly to a wall through damp spraying. 

The part of the chimney that rises above the roof of the 

building, often containing a number of flues. 

The formation of liquid water on a surface from a gas or vapour 

state due to the air temperature falling below its dew point. 

The method of applying insulation above a ceiling in a loft 

space so that everything above the insulation is colder than 

that below, hence the term cold roof. 

A decorative horizontal moulding that runs along the junction 

of internal wall ceilings. 

A Scottish term for a sloping ceiling, the upper side of which 

forms part of the roof of the building. 

Sections of building fabric which have considerably lower 

thermal resistance than neighbouring areas when, for 

instance, an element travels from the interior to the exterior 

surface of a building element or where an area is insufficiently 

well insulated. 

The dew point is the temperature where the water vapour in 

a volume of humid air at a constant barometric pressure will 

condense into liquid water. 

Is the process of reducing air leakage in the frames of 

windows, doors or loft hatches. 

32


Dry Lining: 

Dwang: 

Eaves: 

Geo textile: 

Harling: 

Hemp board: 

Hygroscopic: 

Hydrophobic: 

Jamb: 

Joist: 

Kames: 

Lath and plaster: 

Leaded light: 

LED lighting: 

Lime concrete: 

Mansard roof: 

Mass masonry: 

Mineral paint: 

A wall lining commonly formed of plasterboard on timber 

studs, which does not need to be plastered. 

A Scottish term for a transverse piece of wood inserted 

between joists or posts in order to stiffen them. 

The lower edges of a roof that usually project over a side wall 

in order to carry rain water away from the fabric. 

Geotextiles are moisture vapour permeable artificial fabrics. 

Scottish term for the application of an exterior render of 

roughcast comprised of lime and aggregate. 

A rigid board based insulation formed of fibers from hemp 

plants. Hemp / wool insulation is a semi rigid insulation 

formed of a mixture of hemp and wool fibres. 

A material which can absorb and release moisture. 

Incapable of absorbing moisture. 

The vertical side posts used in the framing of a doorway or 

window. The outer part of the jamb, which is visible, is called 

the reveal. 

A beam supporting the floor or roof, which is normally made 

of timber. 

Strips of lead, which hold the glass in place in a leaded light. 

The building process used for lining internal walls from the 18th 

century up until the mid 20th century. Vertical timber battens 

are fixed to the masonry; thin timber laths are then horizontally 

mounted. Three coats of lime plaster completes this lining. The 

gap behind the laths and plaster is normally 25 – 30mm. 

A window formed of a lattice of small panes and held within 

strips of lead known as kaimes. 

Light-emitting diodes emit visible light when electricity is 

passed through them. They are a form of energy efficient 

lighting. 

A concrete formed of aggregate with lime rather than cement 

as the binder. 

A roof which has two slopes on each side, the lower slope being 

longer and steeper than the other and often incorporating 

dormer windows to allow the roof space to be inhabited. 

Masonry formed of material such as stone, brick or earth 

without a cavity separating the inner and outer parts of the wall. 

A moisture vapour permeable paint finish. 

33


3. Glossary 

Mineral wool insulation: 

A type of thermal insulation made from an inorganic 

fibrous substance that is produced by steam blasting and 

cooling molten glass, slag or rock. 

Water vapour permeable: The ability of water vapour to diffuse through a material. 

Phenolic foam: 

Plaster ‘on the hard’: 

Rafter: 

Relative humidity: 

Reveal: 

Ridge: 

Sarking: 

Secondary glazing: 

Sheep’s wool insulation: 

Sustainability: 

Skew: 

Skirting: 

Solum: 

Staff beads (window): 

Suspended timber floor: 

A synthetic polymer made from thermosetting foam 

plastic and used in thermal insulation. 

The application of lime plaster directly onto the surface 

of masonry walls without any laths. 

A sloping timber extending from the wall plate to the 

ridge of a roof. 

The term used to describe the amount of water vapour 

existing within a mixture of air and water vapour and 

expressed as a percentage. 

The part of the jamb between the frame and the outside 

wall, which is revealed, inasmuch as it is not covered by 

the frame. 

A horizontal line caused by the junction of two sloping 

roof surfaces. 

A continuous layer of timber boards onto which slates 

or tiles are laid. 

A second window installed internally next to the 

original window. 

A flexible insulation formed of wool with a small 

percentage of polyester binder. 

The long term responsible management of resource 

use, encompassing environmental, economic and social 

dimensions to allow for the endurance of said resources. 

Scottish term for the coping stones that run along the top 

of a sloping gable. 

A finishing board, which covers the joint between the wall 

and the floor of a room. 

The vacant area underneath a suspended timber floor. 

A moulded or beaded angle of wood or metal set into the 

corner of plaster walls to protect the external angles of 

the two intersecting surfaces. 

This is a floor suspended above ground level, usually 

consisting of timber joists spanning the ground floor, 

supported by sleeper walls which allows air ventilation 

and prevents dry or wet rot occurring on the timber. 

34


Thermostat: 

Trickle vent: 

U-value: 

Warm roof: 

Window case: 

Window sash: 

Wood fibreboard: 

A device that senses temperature and is used to maintain 

a constant temperature. 

A small opening in a window or building component to 

allow for ventilation, where natural ventilation should 

occur but may be impinged. 

The measurement of the rate of heat loss through a 

building component, the lower the U-value the less heat is 

lost through that building element. U-value is expressed 

in W/m 2 K. 

Insulation is usually placed on or adjacent to the roof 

rafters, so that everything below the insulation is as 

warm as the rooms in the house. 

The framework of a window that holds the sash in place. 

Often referred to as a ‘sash case’. 

The timber frame around the glass in a window. The 

term is used almost exclusively to refer to windows where 

the glazed panels are opened by sliding vertically, or 

horizontally hence the term sash and case window. 

Rigid insulating board, available in various forms and 

is made from a wood based material. 

35

Fabric Improvements for Energy Efficiency in ... - Historic Scotland

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